In view of the fact that polyamide resins are excellent in characteristics such as strength, rigidity, solvent resistance, moldability, and the like, they are used as injection molding materials such as automobile or electric and electronic parts and the like, or packaging materials for foodstuffs, beverages, chemicals, electronic parts, or the like. Above all, polyamides containing an m-xylene group in a polymer principal chain are high in rigidity and also excellent in barrier properties against various gases or chemicals or the like, and hence, they are widely used as injection molding materials or packaging materials.
However, in the polyamides containing an m-xylene group in a polymer principal chain, in view of the fact that a radical is easily formed at the benzyl methyl position from the structural standpoint, they are low in heat stability or heat aging resistance as compared with polyamides such as nylon 6 and the like. For that reason, there are uses to which the polyamides containing an m-xylene group are hardly applied as a molding material, depending upon a severe use environment or condition, for example, a high-temperature environment, etc.
In recent years, in the fields of automobile parts and the like, in which gas barrier properties and heat aging resistance are required, although utilization of polyamides is studied, for the foregoing reasons, it was difficult to apply the polyamides containing an m-xylene group in a polymer principal chain.
For that reason, there are made proposals for improving the heat stability or heat aging resistance of polyamides. For example, Patent Document 1 discloses a heat-resistant polyamide composed of a polyamide containing an m-xylene group in a polymer principal chain, a copper compound, a halide, a hindered phenol and/or a hindered amine, and an organophosphorus compound. However, this method is a method suited for stretched fibers, but it was an unsatisfactory technique for enhancing the heat aging resistance of injection molded articles or extrusion molded articles to be used for automobile parts and the like.
Also, for example, Patent Document 2 proposes a method in which on the occasion of molding processing of a polyamide containing an m-xylene group in a polymer principal chain, at least one member selected from a lubricant, an organophosphorus based stabilizer, a hindered phenol compound, and a hindered amine compound is added in an amount of from 0.005 to 0.5 parts by mass, thereby preventing gelation of the polyamide from occurring. However, this method is a technique for preventing the gelation from occurring during the molding processing, but it was an unsatisfactory technique for enhancing the heat aging resistance after molding.
Also, for example, Patent Document 3 describes, as a molding material for precision parts, an example in which an aromatic secondary amine based compound is incorporated as a heat stabilizer into a polyamide resin. However, this technique is a technique suited for nylon 66, but effects against polyamides having a different polymer skeleton were not reviewed.
In the light of the above, in particular, with respect to the foregoing polyamides having excellent gas barrier properties, it is the present state that a technique for enhancing the heat aging resistance while keeping the gas barrier properties has not been found yet.